Heat oven to 450ºF.Heat oil in medium skillet on medium-low heat. Add onions and sugar; cook 10 to 12 min. or until onions are caramelized, stirring occasionally. Add mushrooms; cook and stir 5 min.Spray baking sheet with cooking spray; sprinkle with cornmeal. Pat pizza dough into 13×9-inch rectangle on prepared bakin….